12 volt LED lamps what is the voltage range?

The 230 volt LED does publish a range of voltages but not the 12 volt version and I wonder if the battery voltage in a caravan is too high?

Battery voltage can raise to 14.8 volts with a stage charger but BS7671:2008 does state 14 volt maximum A721.55.4.1

Fitting a diode will reduce voltage 0.6 volts but then when not on charge it would be under voltage.

Has anyone used standard MR16 LED lamps off a battery and if so were there any problems?

without using a driver i would never go over volts indeed i would tend to aim for 10-15% under the maximum for longevity

i have run a 9-12v led off a 10.8v[12.96 fully charged] lion battery and it far to bright and the only reason it doesnt blow is it drags the voltage down within a few mins so wouldn risk a 12v fully charged at 14.4

The range of safe operating supply voltage depends on how the lamp and / or driver controls the current through the LED element(s).

Simplist current control is a resistor and with that the current directly proportional to applied voltage.

I = (Vs -Vf) / R where Vf is the forward voltage of the LED element which would be between 1.2 and 3.4 volts depending of the type of LED element.

More complex drivers will ( should ) be able to accept a wide range of supply voltages and still put the correct current through the LED element.

I would expect a to see an input range specified for the driver if it was of any reasonable quality.

Until one reverse engineers a 12 volt lamp no idea of what it contains.

Simple 7812 would seem most likely way although at 12 volt likely output more like 11 volt it would ensure it never goes above 12.

However no point re-inventing the wheel so thought would ask if any one had already tried it.

Main problem with 7812 is really should use a heat sink. So will need to select a lamp with a metal base I can drill and screw the 7812 onto with some heat sink compound so a bit of messing around. So if not required then would save me messing around with it.

These are typical PWM driver ICs used in 12V MR16 LED lamps:
http://datasheets.maximintegrated.com/en/ds/MAX16840.pdf
http://www.digchip.com/datasheets/parts/datasheet/838/AMC7150-pdf.php
The ICs can accept an input voltage of up to 40 and 48V respectively. I would not expect 14.8V to be any problem.

I think a DC-DC converter would be useful - it will ensure a constant 12v as the battery fluctuates

As said, you need to be more specific about "12V LED". At one extreme it may have a converter/driver with a wide input range. At the other extreme it may be an array with 3 LEDs in series with a resistor.

They latter will be very sensitive to overvoltage - more than you might think. You may be thinking that 14.8V is "only" 23% over, but that is not the case. When I was "experimenting" with some LED strip I used at work, I found that the LEDs started to light up at around 7V, probably closer to 8V or more once "on". So normally 4V or less is dropped in the resistor. So the current will change by something more like a factor of (14.8-8)/(12-8) which is around 70%
So if you have the "cheapo, uses a resistor" type LEDs, then running them at 14.8 is quite likely to cause "significant age reduction" in the LED chips - they may still work (but will be much brighter), but will be operating well above their ratings and are likely to die sooner rather than later.

I fitted these on a boat.

http://www.ebay.co.uk/itm/GU10-MR16...UK_Home_Garden_Lamps&var=&hash=item1e78b088f1

They work great between 9v - 15v

Thank you "mikely" yes using those drivers clearly will work but "leeco" link is typical GU10 voltage range 85 - 265 volts MR16 just 12 volt.

Not tested white LED but know red one has a 1.2 volt drop across it often used to raise the output voltage from a 7812 voltage reg to 13.2 volts. So removing that fixed voltage it's 10.8 volt to 13.6 volt so 26% overload where resistors are used. This will vary according to voltage of LED I know other colours have different voltages.

Controlling the LED directly is quite easy but when it already has some control built in that makes it harder as any control added could mess up the control inside the bulb.

Since with the chip linked to voltage can fall to 6.5 volt safe method it would seem is to put a 7812 chip in each lamp that limits it to 12 volt maximum and will drop volts around 1 volt so at 11.5 volt still 10.5 volt at lamp.

Yes agree DC to DC would be better but trying to keep it simple. I suppose I could in a way test as if resistors are used then heat is produced but if a switch mode current regulator then less heat is produced so if the switched mode method is used light output will be higher per watt used than if a resistor is used.

So looking at the link from "leeco" then 3W version = 83 lumens per watt and 3.5W version = 100 lumens per watt so likely the 3W one uses resistors and 3.5W uses switch mode supply! However I then started to look at more lamps and range from 50 to 100 lumens per watt.

However we seem to have Lumens - Effective Lumens - RAW Lumens see
this link and this link as a result when we read the information we are not really sure which type of lumens is being quoted so as a result we have really no idea of what lamp type we have.

All MR16 LED lamps have to work over a wide voltage range although the manufacturers have an annoying habit of specifying 12V dead, which is pretty silly. They're designed to work from halogen 12V AC transformers which will show mains fluctuations and will increase voltage with a light load - such as an LED.

Bearing in mind that MR16s work on 12V DC or AC, the maximum DC rating has to be at least the peak AC voltage or 17V. On the odd occasion where a supplier makes a deal of the voltage range for LEDs that will work on 12 or 24V supplies are typically 10-30V DC. eg.

http://uk.alibaba.com/product/1028343373-12V-24V-3-5W-BASE-MR16.html?s=p

As others have said the internal driver is a current source for the LED and effectively performs power conversion, if the input voltage increases the input current decreases and the LED gets the same current and power regardless. I wouldn't worry about putting an MR16 LED on 14.4V - if there is a problem it means that the MR16 is very poor quality indeed.

Take a look at these:

http://www.bedazzled.uk.com/12v_LED_Bulb_Replacement.htm